Spatio-temporal development of surface charges on spacers stressed with DC voltages

The development of surface charge on a right-cylindrical spacer under different DC stress levels is measured in SF₆ for several hours. The DC voltage stress levels are below the stresses where partial discharges with AC voltage generally occur. The measurements indicate that charges are mainly deposited on one side only of the spacer and are predominantly of opposite polarity to that of the applied voltage. The charge and its area increase with time and saturate. Typical saturation times are approximately 3 and 9 h for 10 kV and 5 kV respectively. Magnitudes of saturated charge increase linearly with applied voltage. Various factors which may affect charge accumulation pattern are investigated. Measurements show that charge deposition on a spacer are influenced insignificantly by γ-irradiation or a change of gas from SF₆ to air. However, charge depositions are influenced by surface conductance of the spacer. The charging of the spacer is negligible when stressed with AC and impulse voltages with peak voltages in a range similar to the DC levels used